A bare copper material is conventionally used as a grounding conductor constituting a grounding device. Bare copper materials serving as grounding conductors are arranged in a trench dug in the earth to a predetermined depth, and the copper materials are arranged in a grid pattern in a vertical and horizontal directions. This constitutes a mesh electrode. By way of example, a grounding device having such a mesh electrode is disclosed in the Unexamined Japanese Patent Application Publication (Tokkai-Sho) No. 59-211975.
However, with the conventional grounding device employing metal conductors such as bare copper materials as grounding conductors constituting a mesh electrode as described above, the grounding conductors comprising bare metal conductors are arranged directly in the earth. Accordingly, the corrosion of the grounding conductors comprising bare metal conductors is facilitated by moisture in the soil, the acidity of the soil, the concentration of salt in the soil, and the like. Thus, disadvantageously, the grounding conductors installed in the earth may be subjected to a disconnection or the like, thus spoiling the grounding function of the grounding device.
If the grounding conductors comprising bare metal conductors are covered with a grounding resistance reducing material comprising carbon and cement, the disconnection or the like caused by the corrosion attributed to the soil is unlikely to occur compared to grounding conductors arranged directly in the earth.
These grounding conductors also have a long lifetime. However, the specific resistance of the soil changes rapidly in areas in which the grounding conductors comprising bare metal conductors are not completely covered with the grounding resistance reducing material and in areas in which leaders extend from the ground conductors, and the carbon is very unlikely to be ionized. Consequently, in an electrolytic state such as the one in the soil, contact with the carbon causes the grounding conductors comprising bare metal conductors to be corroded by a battery action resulting from a difference in potential (what is called galvanic corrosion). Disadvantageously, this may cause the disconnection or the like.
Moreover, it has been found that the corrosion is facilitated in areas of the earth in which a direct current is flowing. This is another problem with the conventional grounding conductors comprising bare metal conductors.
It is an object of the present invention to solve the above problems with the conventional grounding conductors.